Freshwater salinization is an emerging threat to aquatic ecosystems across the planet, degrading habitats and negatively impacting wild populations. Deicing practices are a leading cause of freshwater salinization, particularly in the snowbelt region of North America where a variety of salts are widely applied to roads and other surfaces to melt snow and ice. Seasonal pools near roads are considered the most severely impacted aquatic habitats. Runoff into these low water-volume ponds can generate high salinity. Impacts of salt pollution are numerous, ranging from toxicity to population decline to impaired ecosystem function. Here, we investigate a suite of physiological consequences of salinization across multiple life history stages of the wood frog (Rana sylvatica), a pool-dwelling amphibian. Previous work has shown that salinized populations have diverged from unpolluted populations for a suite of physiological, morphological, and reproductive traits, and can experience severe edema (bloating) during the breeding season. Here, we measured swim performance before and after aspirating edema in wild captured wood frogs to show that edema compromises adult aquatic locomotion during breeding. We also found that wood frog mothers from salinized ponds produce ova with inherently higher rates of water uptake compared to mothers from unpolluted pools, consistent with countergradient adaptation, but the ova are smaller. Finally, we found that exposure to road salt inhibits expansion of vitelline membranes in developing embryos and is associated with reduced embryo growth. Together, these results reveal the complexity of population level responses to freshwater salinization, highlighting that impacts occur across multiple life history stages, and that local populations might be evolving adaptations to cope with anthropogenic salinity gradients in freshwater habitats.

Bergmann's and Allen's rules predict changes in body size and appendage length across temperature gradients for species with broad geographic distributions. Larger bodies and longer limbs facilitate cooling whereas smaller bodies and compact limbs limit heat loss. Although these patterns are highly repeatable (hence "rules" of ecology) the patterns and underlying mechanisms are less-well understood in humans. Here I show that variation in running performance among human male triathletes is consistent with both Bergmann's and Allen's rules. Males (but not females) with relatively larger body size and longer limbs performed better at hot compared to cold race venues and vice-versa. Consistent with results in other taxa, sex-specificity may reflect selection for sexual dimorphism. Results suggest that ecological patterns detected over large-spatial scales may arise from fine-scale variation in locomotor performance.

Artificial selection, whether intentional or coincidental, is a common result of conservation policies and natural resource management. To reduce unintended consequences of artificial selection, conservation practitioners must understand both artificial selection gradients on traits of interest and how those traits are correlated with others that may affect population growth and resilience. We investigate how artificial selection on male body size in Pacific salmon (Oncorhynchus spp.) may influence the evolution of female body size and female fitness. While salmon hatchery managers often assume that selection for large males will also produce large females, this may not be the case-in fact, because the fastest-growing males mature earliest and at the smallest size, and because female age at maturity varies little, small males may produce larger females if the genetic architecture of growth rate is the same in both sexes. We explored this possibility by estimating sex-specific heritability values of and natural and artificial selection gradients on length at maturity in four populations representing three species of Pacific salmon. We then used the multivariate breeder's equation to project how artificial selection against small males may affect the evolution of female length and fecundity. Our results indicate that the heritability of length at maturity is greater within than between the sexes and that sire-daughter heritability values are especially small. Salmon hatchery policies should consider these sex-specific quantitative genetic parameters to avoid potential unintended consequences of artificial selection.

Whereas prey tend to reduce conspicuousness, predators remain active to locate their prey. In particular, mesopredators (i.e., predators situated in the middle of two trophic levels) may be subjected to opposing pressures. Locomotor performance influences predator-prey interactions, and together with behavior can be constrained by morphology. In this study, we test how locomotor performance and foraging behavior of larvae of the predaceous amphibian Ambystoma maculatum are influenced by morphology and exposure to chemical cues from predators and competitors. We test whether tail-injured and uninjured larvae differed in morphology, locomotor performance, and feeding rate. Larger individuals showed higher locomotor performance and prey consumption rate. These were not correlated, but the latter increased subsequent locomotor performance. Neither perceived predators nor competitors affected swimming speed or prey consumption rate. Body size was positively correlated with prey consumption rate only in those individuals not previously exposed to chemical cues from predators and competitors. Finally, tail-injured larvae were smaller, but did not experience reduced speed or prey consumption rates.

Human activities have caused massive losses of natural populations across the globe. Like many groups, amphibians have experienced substantial declines worldwide, driven by environmental changes such as habitat conversion, pollution, and disease emergence. Each of these drivers is often found in close association with the presence of roads. Here we report a novel consequence of roads affecting an amphibian native to much of North America, the wood frog (Rana sylvatica). Across 38 populations distributed from southern to central New England, we found that adult wood frogs living adjacent to roads had higher incidence and severity of oedema (indicated by obvious bloating caused by subcutaneous fluid accumulation) during the breeding season than frogs living away from the influence of roads. This effect was best explained by increased conductivity of breeding ponds, probably caused by runoff pollution from road salt used for de-icing. Oedema severity was negatively correlated with locomotor performance in more northerly populations. Interestingly, northern populations experience more intense winters, which tends to result in more de-icing salt runoff and increased energetic demands associated with overwintering cryoprotection needs. Thus, this emerging consequence of roads appears to impose potential fitness costs associated with locomotion, and these effects might be most impactful on populations living in regions where de-icing is most intense. Together, our findings reveal a novel set of impacts of roads and runoff pollution on wood frog physiology and performance, which seem likely to contribute to population decline. Given the global prevalence of roads and increasing salinisation of freshwater habitats, oedema and related impacts could be widespread consequences faced by amphibian populations across much of the planet's temperate zones.

Erik I. Svensson,1,2 Pauline Blaimont,3 Ryan Calsbeek,4 Lesley T. Lancaster,5 Andrew McAdam,6 and Suzanne C. Mills7,8 1Evolutionary Ecology Unit, Department of Biology, Lund University, Lund SE-223 62, Sweden 2E-mail: erik.svensson@biol.lu.se 3Department of Biology, Behavioral Neuroscience and Health Sciences, Rider University, Lawrenceville, New Jersey 08648 4Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 5School of Biological SciencesUniversity of Aberdeen, Aberdeen AB24 2TZ, UK 6Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309 7PSL Université Paris, EPHE-UPVD-CNRS, USR 3278 CRIOBE, 98729 Papetoai, Moorea, French Polynesia 8Laboratoire d’Excellence, CORAIL, 58 avenue Paul Alduy, CEDEX 668 60, France

A limitation in bioacoustic studies has been the inability to differentiate individual sonic contributions from group-level dynamics. We present a novel application of acoustic camera technology to investigate how individual wood frogs' calls influence chorus properties, and how variation influences mating opportunities. We recorded mating calls and used playback trials to gauge preference for different chorus types in the laboratory. Males and females preferred chorus playbacks with low variance in dominant frequency. Females preferred choruses with low mean peak frequency. Field studies revealed more egg masses laid in ponds where males chorused with low variance in dominant frequency. We also noted a trend towards more egg masses laid in ponds where males called with low mean frequency. Nearest-neighbour distances influenced call timing (neighbours called in succession) and distances increased with variance in chorus frequency. Results highlight the potential fitness implications of individual-level contributions to a bioacoustic signal produced by groups.

The efficacy of most biological processes is temperature dependent and, within physiological limits, on average, warmer is better. This axiom of biology has led to a wide range of adaptations for dealing with temperatures that are outside of an organism’s preferred temperature. Many pond-breeding amphibians lay their eggs during early spring, when water temperatures are near freezing. Communal nest-site selection has been proposed as a mechanism to increase developmental temperatures, and temperatures near the center of egg-mass aggregations are elevated relative to egg-masses on the aggregation’s periphery. It is unclear whether this spatial variation in temperature is due to concentration of metabolic heat, absorption of solar radiation, or both. Here, we explore finer scale spatial variation within egg masses of the wood frog Rana sylvatica, one of the earliest amphibians to breed during the North American spring. We compared peripheral and core temperatures of egg masses that were exposed either to 1) ambient sunlight from above, or 2) sunlight reflected by a mirror from below. We found that differences between core and peripheral temperatures were higher in the control than in the mirror treatment, but core and peripheral temperatures were statistically indistinguishable in both cases. Moreover, the difference in peripheral and internal temperatures increased significantly over the course of development. However, these trends were only significant in ambient sunlight and actually decreased in the mirror group. Our results suggest that the benefits of communal nesting are also experienced by individual egg masses, albeit to a lesser extent. In addition, the lack of effect in shaded egg masses suggests that the thermal advantage is tied to sun exposure and not due to concentration of metabolic heat.

Paul Argenti and Ryan Calsbeek of Dartmouth explain that corporations should focus not on their rankings, but on the attributes that influence those rankings. They combine evolutionary biology and corporate reputation research to determine what makes a company the best that it can be, arguing that a more scientific approach to corporate success is needed.

Trade-offs between reproduction and survival are central to life-history theory and are expected to shape patterns of phenotypic selection, but the ecological factors structuring these trade-offs and resultant patterns of selection are generally unknown. We manipulated reproductive investment and predation regime in island populations of brown anole lizards (Anolis sagrei) to test (1) whether previously documented increases in the survival of experimentally non-reproductive females (OVX = ovariectomy) reflect the greater susceptibility of reproductive females (SHAM = control) to predation and (2) whether phenotypic selection differs as a function of reproductive investment and predation regime. OVX females exceeded SHAM controls in growth, mass gain and body condition, indicating pronounced energetic costs of reproduction. Although mortality was greatest in the presence of bird and snake predators, differences in survival between OVX and SHAM were unrelated to predation regime, as were patterns of natural selection on body size. Instead, we found that body condition at the conclusion of the experiment differed significantly across populations, suggesting that local environments varied in their ability to support mass gain and positive energy balance. As mean body condition improved across populations, the magnitude of the survival cost of reproduction increased, linear selection on body size shifted from positive to negative, and quadratic selection shifted from stabilizing to weakly disruptive. Our results suggest that reproductive trade-offs and patterns of phenotypic selection in female brown anoles are more sensitive to inferred variation in environmental quality than to experimentally induced variation in predation.

Alternative reproductive tactics (ARTs) are ubiquitous throughout the animal kingdom. Multiple mechanisms have been proposed to explain the maintenance of ARTs over time, including disruptive and negative frequency-dependent selection and female choice. However, these mechanisms focus exclusively on selection in the sex exhibiting the polymorphism, potentially limiting our understanding of the evolutionary causes and consequences of ARTs. Here we explore the role that intralocus sexual conflict may play in the maintenance of sex-specific ARTs. We use a genetically explicit individual-based model in which female fecundity and male tactic share a genetic architecture. By modeling ART maintenance under varying selection regimes and levels of sex-specific gene expression, we explore the conditions under which intralocus sexual conflict can maintain a hypothetical ART defined by two color morphs that depend on an underlying liability trait. Our models consistently revealed that sexual conflict can result in the persistence of a sex-specific polymorphism over hundreds of generations, even in the absence of negative frequency-dependent selection. ARTs were maintained through correlated selection when one male ART has lower fitness but produces daughters with higher fitness. Importantly, the maintenance of ARTs through sexual conflict resulted in a significant reduction in population growth rate, indicating that the evolutionary mechanism of ART maintenance can have broad ecological consequences. These results highlight the importance of understanding selection on both sexes when attempting to explain the maintenance of ARTs. Our results are consistent with a growing literature documenting genetic correlations between male ARTs and female fitness, suggesting that the maintenance of sex-specific ARTs through intralocus sexual conflict may be common and widespread in nature.

Abstract Intralocus sexual conflict, which arises when the same trait has different fitness optima in males and females, reduces population growth rates. Recently, evolutionary biologists have recognized that intralocus conflict can occur between morphs or reproductive tactics within a sex and that intralocus tactical conflict might constrain tactical dimorphism and population growth rates just as intralocus sexual conflict constrains sexual dimorphism and population growth rates. However, research has only recently focused on sexual and tactical intralocus conflict simultaneously, and there is no formal theory connecting the two. We present a graphical model of how tactical and sexual conflict over the same trait could constrain both sexual and tactical dimorphisms. We then use Coho salmon (Oncorhynchus kisutch), an important species currently protected under the Endangered Species Act, to investigate the possibility of simultaneous sexual and tactical conflict. Larger Coho males gain access to females through fighting while smaller males are favored through sneaking tactics, and female reproductive success is positively correlated with length. We tested for antagonistic selection on length at maturity among sexes and tactics and then used parent–offspring regression to calculate sex‐ and tactic‐specific heritabilities to determine whether and where intralocus conflict exists. Selection on length varied in intensity and form among tactics and years. Length was heritable between dams and daughters (h2 ± 95% CI = 0.361 ± 0.252) and between fighter males and their fighter sons (0.867 ± 0.312), but no other heritabilities differed significantly from zero. The lack of intertactical heritabilities in this system, combined with similar selection on length among tactics, suggests the absence of intralocus conflict between sexes and among tactics, allowing for the evolution of sexual and tactical dimorphisms. Our results suggest that Coho salmon populations are unlikely to be constrained by intralocus conflict or artificial selection on male tactic.

Animal coloration is a multifaceted trait with many ecological roles and related to a variety of developmental and physiological processes. Consequently, coloration is often subject to a variety of selective pressures, leading to the evolutionary maintenance of variation. In this study, we investigated hypotheses related to the maintenance of dorsal color variation in wood frogs (Rana sylvatica). First, we tested for multimodality, and whether color correlates with body size or condition or varies by sex or age class. We combined behavioral trials with visual modeling to test for sex recognition. We also considered visual models for predators and tested for an interaction between discriminability indexes (JND) of color channel (chromatic vs. achromatic) and predator type (birds vs. snakes), as well as for a within individual trade-off between the JND of chromatic and achromatic coloration. Finally, we tested for disruptive viability selection on color using predation trials, and for antagonistic directional selection between viability selection and reproductive investment of females. We found that wood frogs present continuous color variation that does not correlate with body size or condition, but that changes with age. Wood frogs present subtle sexual dichromatism, but we found no evidence for a role of color in sex recognition. Instead, we discuss the possibility that sex differences might, at least in part, have a demographic explanation. Predator visual models indicated that wood frogs cannot solely rely on dorsal coloration for camouflage. Moreover, different predators might present selective pressures in different color channels, while individuals' achromatic and chromatic coloration trade-off in JND. Therefore, different selective pressures caused by different predators might interact with ontogenetic changes and developmental/physiological trade-offs to maintain color variation. We found no relationship between color and survival or reproductive investment, suggesting further work is required to fully understand selection on color. Our results highlight the importance of understanding evolutionary trade-offs and developmental/physiological constraints in combination with one another, and suggest the potential for an interaction between these proximate and ultimate mechanisms in the evolutionary maintenance of variation. These results likely extend beyond color expression in amphibians, and exemplify a more general process for such evolutionary outcomes.

Human activities have caused massive losses of natural populations across the globe. Like many groups, amphibians have experienced substantial declines worldwide, driven by environmental changes such as habitat conversion, pollution, and disease emergence. Each of these drivers is often found in close association with the presence of roads. Here we report a novel consequence of roads affecting an amphibian native to much of North America, the wood frog ( Rana sylvatica ). Across 38 populations distributed from southern to central New England, we found that adult wood frogs living adjacent to roads had higher incidence and severity of edema (bloating caused by fluid accumulation) during the breeding season than frogs living away from the influence of roads. This effect was best explained by increased conductivity of breeding ponds, caused by runoff pollution from road salt used for de-icing. Edema severity was negatively correlated with locomotor performance in more northerly populations. Interestingly, northern populations experience more intense winters, which tends to result in more de-icing salt runoff and increased energetic demands associated with overwintering cryoprotection needs. Thus, this emerging consequence of roads appears to impose potential fitness costs associated with locomotion, and these effects might be most impactful on populations living in regions where de-icing is most intense.

INTRODUCTION:Trade-offs are widespread in biological systems. Any investment in one trait must necessarily limit the investment in other traits. Still, many studies of physiological performance produce positive correlations between traits that are expected to trade-off with one another. Here we investigate why predicted trade-offs may often go unmeasured in studies of human athletes. METHODS:Triathletes compete in consecutive swimming, cycling, and running events as a single competition, events whose physical demands may be especially prone to generating performance trade-offs. Performance variation in these three events interacts to explain overall variation in athletic performance. RESULTS:We show that individual variation in athletic performance can mask trade-offs among disciplines, giving the impression that high-performance triathletes are athletic generalists. Covariance in race performance across the three disciplines was positive in the most elite athletes but became increasingly negative as race times increased. CONCLUSIONS:These performance trade-offs among the disciplines preclude the realization of a generalist athlete except in the most elite triathletes, a result similar to the "big houses, big cars" phenomenon in life history evolution. This distinction between trait combinations that are favored for optimal performance versus constrained by trade-offs was only apparent when accounting for individual level variation in athletic performance. Our results provide further evidence that meaningful trade-offs may be missed if individual variation in quality is disregarded.

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Whenever genetically correlated traits experience antagonistic selection, an adaptive response in one trait can lead to a maladaptive response in the correlated trait. This is a form of genome-level conflict that can have important evolutionary consequences by impeding organisms from reaching their adaptive optima. Antagonistic selection should be pervasive in organisms with complex life histories because larval and adult life stages specialize in dramatically different environments. Since individuals express larval and adult morphologies from a single genome, genomic conflict across ontogenetic stages should also be prevalent. Using wood frogs as a study system, we measured natural selection on larval and postmetamorphic life stages and estimated genetic correlations among traits. Alternative life stages experienced a mix of both antagonistic and congruent viability selection. The integration between traits changed over the course of metamorphosis, reducing genetic correlations that cause conflict. Our results provide novel experimental evidence that metamorphosis can alleviate genomic conflict by partitioning life-history stages into modules that can more readily respond to selection. These results highlight the adaptive potential of metamorphosis as a means to avoid ecological specialization trade-offs. Moreover, they provide insights into the prevalence and evolutionary maintenance of complex life cycles.

In animals, color signals that convey information about quality are often associated with costs linked to the expression of coloration and may therefore be honest signals of sender quality. Honest indicators are often seen in sexual signals that are used by males to advertise quality to females. Carotenoid and pterin pigments are responsible for yellow, orange, and red coloration in a variety of taxa, but can also serve important roles as antioxidants by reducing free radicals in the body. In this study, we test the effects of a novel full-bodied orange color phenotype of the brown anole, Anolis sagrei, on mate choice, physiology, and survival. We found no evidence that lizards expressing the orange phenotype were preferred by females. Additionally, they did not differ in immune function, running endurance, or maximum sprint speed from lizards that did not express the novel phenotype. Pigment extractions revealed that orange body coloration resulted from pterin pigments and not carotenoids. Visual models suggest that the orange phenotype is less conspicuous to bird predators than the brown phenotype and may provide an adaptive explanation for the persistence of this trait. Given its small, yet positive effect on fitness, we expect the orange color phenotype to increase in frequency in subsequent decades.

The maternal allocation of carotenoids to eggs has been widely documented and manipulated. However, it is often assumed that the sole adaptive value of this allocation is to increase offspring fitness. Because carotenoids can be pro-oxidants or antioxidants depending on their concentrations and their chemical environment (i.e. presence of other antioxidants), dams may need to dispose of excess carotenoids upon depletion of other antioxidants to prevent oxidative damage. Additionally, the amount of carotenoids deposited in eggs may be dependent on male traits such as quality and coloration. We evaluated these two non-mutually exclusive hypotheses for carotenoid allocation to eggs and assessed paternal effects by supplementing male and female brown anole lizards, Anolis sagrei, with dietary carotenoids or with a combination of carotenoids and vitamin C. We found significant differences in the antioxidant capacities of fertilized and unfertilized eggs produced by female lizards, but the treatment did not affect the antioxidant capacity or carotenoid content of eggs. However, the carotenoid concentration of unfertilized eggs from carotenoid-supplemented females was significantly higher than eggs from the control group. Male coloration and body size did not affect the antioxidant capacity or carotenoid content of the eggs. Carotenoids may be allocated to unfertilized eggs to offset oxidative damage to the dam, with a neutral effect on offspring, rather than to solely provide antioxidant benefits to offspring as has been widely assumed.